6CW5 amps

[EWBrown]

From the "kasuga" website:

6CW5 / EL86 PP amp:

http://www.e-kasuga.net/amp_pdf1/6cw5pp.pdf

6CW5 / EL86 SE "Cathode" amp:


http://www.e-kasuga.net/amp_pdf1/6CW5-cathode-amp.pdf

[Geek]

Ahhhh, one of my favourite tubes!

The 6CW5 is a great PP tube and you don't need gobs of B+ to run it.

Some of my (mis)adventures
http://geek.scorpiorising.ca/GeeK_ZonE/ ... pic=4706.0

[EWBrown]

Now, that's definitely a unique and original approach!

Have you tried 6CW5 in triode strapped mode?

I have 6CW5 / EL86 "triode" data, two different versions:

1: gm= 7.5 mA/V, RP = 1K, mu = 7.5, VA = 200 V, max I = 100 mA PD = 12 W, no g1 bias voltage stated (Tom's data)

2: gm = 12 mA/V, RP = 667 ohms, mu = 8, VA = 170 V, Vg1 -12.5V, IP = 74 mA, PD = 12 W

I have several assorted 6CW5s, 10CW5s, and a nice matched quad of Brimar PL84 (15CW5) which one of the NNETG'ers gave me several years ago.

/ed B

[Geek]

Have you tried 6CW5 in triode strapped mode?

Yep! Them screens look like a Sunbeam toaster above 150V

I have 6CW5 / EL86 "triode" data, two different versions:

1: gm= 7.5 mA/V, RP = 1K, mu = 7.5, VA = 200 V, max I = 100 mA PD = 12 W (no g1 voltage stated)

2: gm = 12 mA/V, RP = 667 ohms, mu = 8, VA = 170 V, Vg1 -12.5V, IP = 74m A, PD = 12 W

Do you have Tom Schlangen's triode curves of the tube?

[EWBrown]

One of the 6CW5 triode strapped data was Tom's, theother was from a source that I don't recall, and, no, I don't have Tom's curves.

For a power tranny, I'd use a 120:120 isolation tranny, with a FWB, it would give me around 160VDC, and all of the current I'd ever need to light 'em up

I've seen the 4.5W EL86 SRPP design, just might breadboard up one channel and give it a listen.
With its 1K output impedance, I could use a 70V line matcher and 8 ohm speaker.

/ed B

[EWBrown]

I've seen a few designs using horizontal sweep tubes (6AV5GA, 6GE5, etc) , with the screen grid driven - this requires a rather hefty drive signal - and G1 simply has the bias voltage applied. Think in terms of driving the control grid of a 6S19P, 6S41C or 6C33C

This works well with pentodes with low (150 to 200V maximum) screen voltage ratings, and not so well with those which have higher G2 voltage.

Might this technique be applicable to the 6CW5

Update 8 April 2013:


Its application with 6AV5GAs is covered at the end of this "Tube Lab" article: http://www.tubelab.com/6AV5.htm

It seems to be a lot more applicable to PP rather than to SE, as it can drive the output tubes well into Class B.

/ed B

[Geek]

Give it a whirl!

Tom had sent me a bunch to test them as class-A2, but they didn't like to draw grid current Didn't think of trying to drive the screen

[soundbrigade]

I thought I had a quad of this tube but it was another one (E80L). I think very many sets were built using this tube in an PP-config and w/o iron but using an 800 Ohm speaker.
I have a schematic here: http://www.pastisch.se/EF/img911.jpg of a typical amplifier.

[Geek]

Actually... if you SRPP it with some high Va and parafeed the output as per Yves Monmagnon's design, he's obtained 25W out of it (as I have in traditional PP).

*edit*

Now, that's definitely a unique and original approach!

Thank you!!!

That method of UL-making was inspired by a fellow DIY'er.... whose name escapes me at the moment
(I just "Goldberged" it )

[EWBrown]

I'd just ditch the tone stack and input selector, and go with this essential part of the 6CW5 design:



And change C9 to an 8.2 uF 400V Solen (or similar film cap), just because electrolytics truly stynque as signal couplers...

The ECC83/12AX7 VA has more gain than would be needed, perhaps a 6CG7 or 6GU7 would serve better as the VA stage,
with appropriate resistor value adjustments.

I don't read Swedish, but I could gather from the schematic and printed description, that the NFB reduces the THD from 10% @ 5W to less than 1% THD.

/ed B